The present invention relates to an authoring system for: variously processing a bitstream carrying video information representing individual titles having content with a particular sequential relationship, audio data, and ancillary video data; generating a bitstream whereby a title with user-selectable content can be constructed; efficiently recording to a particular recording medium the generated bitstream; and reproducing title content according to a user-selected sequence from the generated bitstream. More specifically, the present invention relates to a method for generating a multimedia stream comprising mutually related audio data and video data, and to a multimedia optical disk authoring system for storing the multimedia stream as digital data.
Authoring systems that are part of systems using analog video and video CDs for producing titles having content with a particular sequential relationship by digitally processing multimedia data such as video data, audio data, and ancillary video data have been developed in recent years. MPEG data is one example of a multimedia stream comprising such audio information and video information. MPEG data recording media include Video CD, and an authoring system therefor is based on a workstation. A Video CD system is able to record video data to a CD medium, which is usually used for digital audio recording and has a recording capacity of approximately 600 megabytes, by using a high efficiency MPEG video compression method.
In this type of authoring system, elementary streams of video and audio information are first encoded, and then system stream encoding is applied to these elementary streams to generate an MPEG stream. A reproduction path, which is a reproduction sequence of an MPEG stream, is then determined to enable reproduction of content according to a user-selected scenario. This scenario information and MPEG stream are then multiplexed, converted to a disc image of the CD medium, and then recorded to a CD medium to create a master disc. This master disc is then duplicated by means of a pressing process or other method to produce discs for distribution.
More recently, an optical disc recording medium known as DVD has been introduced with a greater storage capacity than Video CD. Video with an extended play time can be stored to DVD media, and this capacity can be used to achieve such desirable, but conventionally unavailable functions, as an alternative path playback function for video data. Alternative path playback is a function whereby video data from plural related paths is divided into specific segments, which are then multiplexed on an optical disc. A disc reproduction apparatus then reproduces only the video data segments selected from among a plurality of multiplexed video data segments, skipping those multiplexed segments not associated with a selected reproduction path. These multiplexed sections are called xe2x80x9calternative video reproduction periods.xe2x80x9d
An example of an alternative reproduction function is the parental lock playback function whereby the playback video is selectively reproduced according to viewing restriction information. More specifically, this function enables the selective presentation or non-presentation of, for example, violent scenes in a movie. A further example of an applied alternative reproduction function is multi-viewpoint playback in which images from different viewing angles are selectively reproduced. A specific example of this is a baseball game in which the imaging angle of the video playback can be selectively changed during a live broadcast to images presented from, for example, the batter""s viewpoint, the pitcher""s viewpoint, or the viewpoint of a spectator""s seat.
Because alternative video reproduction periods are skipped during playback, associated video data must satisfy a wide range of restrictive conditions relating to encoder conditions and video data combinations. However, conventional Video CD and other authoring system processes, in principle, generate all MPEG data according to the same conditions. As a result, directly applying this process will result in the generation of defective alternative video reproduction periods due to video data not satisfying these conditions. Discs containing such defective alternative video reproduction periods will cause the disc reproduction apparatus to malfunction during playback.
Furthermore, such defective alternative video reproduction periods cannot be detected until the segment is played back after the master disc is completed. As a result, the title producer must re-author the master disc starting from the encoding process, imposing a significant burden. The magnitude of this burden is particularly severe during MPEG-2 encoding. MPEG-2 encoding, in general, provides significantly higher quality audio and video streams compared with MPEG-1, and the playback time is approximately double. This is because the video quality in MPEG-2 is determined by such factors as the bit rate and other parameters specified during encoding, and by the filters used. A two-pass encoding process is therefore used. In this two-pass process, the encoded image quality is checked, parameters are readjusted to achieve the image quality that can be provided with MPEG-2, and the final image is then produced through a second encoding pass. As will thus be obvious, a significant amount of work is required to generate a multimedia stream containing alternative video reproduction periods.
The compression method and data syntax of MPEG-2 are also slightly different from those used in MPEG-1. The content of and differences between MPEG-1 and MPEG-2 are described in detail in the MPEG standards ISO-11172 and ISO-13818, and further description thereof is thus omitted below. While the structure of the video encoding stream is defined in MPEG-2, a hierarchical structure for the system stream and a method for processing low hierarchy levels are not clearly defined.
In consideration of the above problem, an object of the present invention is to provide a generating method for efficiently generating a multimedia stream containing alternative video reproduction periods and an authoring system therefor. The invention relates to an authoring system for generating a bitstream constituting a title having content corresponding to a user selection by applying a variety of processes to a source stream carrying video data, audio data, and ancillary video data constituting titles having content with a particular sequential relationship. The authoring system comprising a means for presenting source stream content in editing units, and a means for generating edit command data for the presented editing units (VOB).